1. Field of the Invention
The present invention relates to preparation of mixtures rich in 3,4,5,6-tetrachloro-2-trichloromethyl pyridine by chlorination in the presence of ferric chloride catalyst of 3,4,5-trichloro-2-trichloromethyl pyridine, 3,5-dichloro-2-trichloromethyl pyridine or 5-chloro-2-trichloromethyl pyridine, or mixtures thereof. Mixtures rich in 3,4,5,6-tetrachloro-2-trichloromethyl pyridine are useful as intermediates in the preparation of agricultural chemicals, especially herbicides.
2. Description of the Prior Art
The present invention concerns the preparation of mixtures rich in 3,4,5,6-tetrachloro-2-trichloromethyl pyridine by the reaction of 5-chloro, 3,5-dichloro, or 3,4,5-trichloro-2-trichloromethyl pyridine, or mixtures thereof, with gaseous chlorine at temperatures from 170.degree. C. to 220.degree. C. in the presence of ferric chloride catalyst. 3,4,5,6-tetrachloride-2-trichloromethyl pyridine has utility as an intermediate in herbicides such as those described in Redemann U.S. Pat. No. 3,234,229. Norton et al U.S. Pat. No. 3,256,167 describes a process for manufacturing 3,4,5,6-tetrachloro-2-trichloromethyl pyridine by reacting alpha-picoline hydrochloride with chlorine between 95.degree. C. and 120.degree. C. Molar yields of 27% of 3,4,5,6-tetrachloro-2-trichloromethyl pyridine are taught in Johnston et al U.S. Pat. No. 3,418,323 by ultraviolet light catalyzed chlorination of 3,4,5-trichloro-2-trichloromethyl pyridine at 150.degree. C. Johnston et al U.S. Pat. No. 3,186,994 teaches the ultraviolet catalyzed chlorination of 3,4,5-trichloro-2-trichloromethyl pyridine at 250.degree. C. to yield pentachloropyridine. There is no prior disclosure known to applicants which teaches the production of 3,4,5,6-tetrachloro-2-trichloromethyl pyridine by chlorination of 5-chloro or 3,5-dichloro-2-trichloromethyl pyridine.